1. Field of the Invention
The present invention relates to gas turbine engines for powering automotive and other vehicles and, more particularly, to a gas turbine engine having a multi-stage stator assembly for controlling the forward and reverse motion of the output shaft of the turbine, including a neutral position between a forward and reverse stage of the multi-stage stator assembly, and provides a servo mechanical control for accurately positioning the multi-stage stator assembly in a decelerating position when desired, and for maintaining the multi-stage stator assembly in the neutral position when the vehicle is stationary.
2. Description of the Prior Art
It is known in turbine engines to provide adjustability in the nozzle blades which direct the flow of the gases to the blades of the turbine rotor, in a manner such that the angle of incidence of the stator vanes relative to the turbine blades is most suitable for maximum efficiency at different speeds and loads. Such adjustability has been accomplished by rotating the blades on their central axis to effect the flow path therebetween. Such stator vanes have been rotated by means of inner and outer gear rings, levers, or cam devices to accomplish different incidence angles relative to the turbine wheel. To function well, the trailing edge of the stator vanes must come as close as possible to the outer ends of the turbine vanes, such as to favor laminar flow. However, the stator vanes must be spaced sufficiently distant from the outer ends of the turbine vanes so as not to interfere therewith as the stator vanes pivot. Thus, substantial leakage occurs between the stator vanes and the turbine blades at some angular positions of the stator vanes. A disadvantage of such devices is that their designs often fail to prevent leakage of gases between the end portions of the stator vanes and their inner and outer mounting rings and, consequently, prevent precise and positive control of the turbine. In addition, such parts often are subjected to substantial vibration, flutter, wear, and seizure. Moreover, designs of this type are costly to fabricate and assemble, and have been very expensive to maintain. Finally, the shape of the pivotable stator vane, when used for reverse motion, does not provide for a smooth and efficient transfer of power to the turbine engine.
The above described prior art is exemplified by the following patents:
______________________________________ COUNTRY PATENT NO. ISSUED ______________________________________ United States 3,232,581 February 1, 1966 United States 3,243,159 March 29, 1966 United States 3,972,644 August 3, 1976 United States 4,003,199 January 18, 1977 ______________________________________
These prior art arrangements for varying the positions of vanes in a stator assembly in a radial inflow turbine are usually only good for one position and have been found to be inadequate to properly and precisely control the flow of gases to the turbine wheel of the turbine, for varying speed and loads.
It is also known in turbine engines to provide a multi-stage stator assembly having a plurality of sets of stator vanes, each having a different fixed angle of incidence. The multi-stage stator assembly is adjustably positionable axially relative to the turbine blades such as to bring any preselected one of the sets of stator vanes into operative alignment with the turbine blades. Such adjustability of the position of the multi-stage stator assembly is accomplished by various driving means to securely position the multi-stage stator assembly in one of a limited number of discrete preselected operating positions, each corresponding to the alignment of one of the sets of stator vanes with the turbine blades. A disadvantage of such devices is that their designs only provide for a small predetermined number of power levels and, accordingly, a smooth transition between these positions is often unavailable. Furthermore, due to the existence of such discrete preselected operating positions, the responsiveness of the turbine engine to differing speeds and loads is somewhat limited.
The above described prior art is exemplified by the following patents:
______________________________________ COUNTRY PATENT NO. ISSUED ______________________________________ United States 2,421,445 June 3, 1947 United States 4,220,008 September 2, 1980 Great Britain 738,987 October 26, 1955 Great Britain 753,316 July 25, 1956 France 986,680 August 3, 1951 France 1,084,552 January 20, 1955 ______________________________________
In the parent application to the present continuation-in-part application, it was proposed to provide a multi-stage stator assembly having a reverse stage and a plurality of discrete forward stages. However, unlike the prior art, the parent application provided for the adjustable selective positioning of the multi-stage stator assembly in any of the continuous positions between the full reverse stage and the lowest output forward stage, so as to provide a continuously and smoothly variable selection of output. In the parent application, the precise positioning of the multi-stage stator assembly relative to the turbine blades was accomplished either by means of a piston cylinder arrangement or by a crank arm arrangement.
Furthermore, in the parent application, a neutral position was provided for, disposed approximately midway between the full reverse position and the first forward stage of the multi-stage stator assembly.